Strange Transmission Issue

I've been searching the net for the past week and a half now for somebody with the same issue as I now have, but I've had no luck.

Here's the situation:
I let somebody use my truck for hauling some furniture one day, and when I got it back I came across a transmission issue that was not there before. ( not that it had any issues before. )

I have the three speed automatic with overdrive in my 91 chev pickup. I generally use the tranny to slow the truck down when driving due to crap brake pads and the awesome sound of straight pipes. However, after I got my truck back I noticed that when I dropped it down a gear... nothing would happen... the truck would just coast until I applied throttle.
This goes for every gear, shifting from OD to D, D to 2nd, and 2nd to 1st. The truck Will NOT *manually* shift down.

Now it would seem normal to have messed something up that it would not shift into a gear, but that doesn't seem to be the case. When I am in drive, the truck will shift up and down perfectly when and where it needs to, and I can hold the truck in a specific gear by shifting *up* to it manually, if I so choose. I just cannot shift down to slow the truck down.
It goes into gear by itself at the correct RPM every time and it shifts smooth.

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So besides the down shifting issue, here is whats confusing me the most.

Before - I could put the truck in first and speed up to 40, ( or shift down from a higher gear ) then let off the gas and the use the tranny and the engine to slow the truck down again. The most noticeable thing would be the nice sound the truck made, and that I could slow down in a tenth the distance than I could with just my crappy brakes.

Now - I can put the truck in first gear and speed up to 40, but when I let off the gas... the truck just coasts. The truck is Still In First gear and the engine should thus work as a brake when i let off... but there is no resistance at all. If I apply throttle, it speeds up, but dropping the engine RPM no longer slows the vehicle at all... This is confusing the **** out of me because I have not seen this happen before and cannot understand how that's even possible, even though it's probably something stupidly obvious.

As far as I was aware, the transmission is a direct input-output setup, with the addition of the torque converter. So if you spin one end then the other end will spin, regardless of which end you turn. It seems to me that it's behaving in such a way that the input drives the output fine, but when you spin the output, the input does nothing.

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I've done extensive work to many vehicles, but automatic transmissions are not something I specialize in... obviously.
If anybody could give me some pointers, or point me to a thread that I've obviously missed, it would be greatly appreciated.

Not really hard to guess what happened here. You burned up the torque converter with all your manual downshifting. It of course didn't rear its ugly head until you got your truck back from your friend -- but make no mistake... you burned it up. You can't drive a stock automatic like a manual transmission. You need to spend some serious coin on your transmission to be able to do that.

You drive a truck that weighs in at near 5000 pounds with "crappy" brakes and rely on the transmission to slow you down? Get the brakes fixed, or get it off the road man. Seriously, your "sweet" exhaust noise is no excuse for jeopardizing someone else's life because you have bad brakes Crappy brake pads... come on man. Decent ones are less than $55 for both sides at Canadian Tire or Parts Source Plus. Certified Semi-Metallic. You have no excuse for not having brakes. None what so ever. Fix your brakes before you fix your transmission.

Quite condemning, but thank you for your reply. Not that this helps my case any, but I weighed the truck and it came to 6100lbs with an empty box. I was a bit confused as to why a half ton would be so heavy, but to be honest, I don't much care.

Regardless, I was going to drop a 5 speed in the truck anyways and now would be the optimal time, wouldn't you think?
At the very least, when something blows up in a standard transmission, it doesn't take much to figure out what.

Quite condemning, but thank you for your reply. Not that this helps my case any, but I weighed the truck and it came to 6100lbs with an empty box. I was a bit confused as to why a half ton would be so heavy, but to be honest, I don't much care.

Regardless, I was going to drop a 5 speed in the truck anyways and now would be the optimal time, wouldn't you think?
At the very least, when something blows up in a standard transmission, it doesn't take much to figure out what.

Click to expand...

I hate to be _that_ guy... but sometimes sugar coating things makes it worse. You can keep driving an automatic like a manual without damaging it, and continue gearing up/down manually, and engine braking -- you really need a manual valvebody/shift kit, and a heavy-duty version of your torque converter (stock-1500 RPM stall). You don't need a "built" transmission if your engine is stock/mild. It just needs to be setup for manual shifts and high loads... the TC is like a clutch but it absorbs so much more of the lunging motion a rear wheel drive vehicle creates when performing high rpm downshifts (if aren't racing and rpm matching your downshifts hehehe). Hence the need for the HD/Towing TC for a street truck. It won't make driving sloppy or ridiculous to get moving without revving the piss out of it. And, you'll be able to row through the gears all day long. But please, fix your brakes.

If the trans is stock, it can't take that kind of abuse for long. The TC eventually gets cooked, kinda like a burnt clutch.

I know its fun to drive like this, I am certainly no model citizen. I do it myself from time to time, and it cost me a transmission. But you learn and adapt. I don't always drive like that anymore, even though I have a 4L60E built for a bit of abuse (not serious abuse, but I can play). Favour the brakes a lot more and still downshift manually. Keeping the ride a bit smoother and keep the downshifts from going into the higher RPMs. I aim for the 2000-2500 RPM sweet spot for re-acceleration while "working" traffic. Even a stock transmission can handle that -- it is like you're towing. As you said.. 6100 lbs.. you're a full size car, towing a small compact car all the time.

If you have plans for a 5spd swap, that's great! Yes, now would certainly be the time. You'll certainly be able to have more fun driving it the way you do, you have two more gears. You'd probably want a beefier clutch and flywheel setup if you like high RPM downshifting all the time.

Just sayin...I've broken a few transmissions... mostly because stock can't handle daily enthusiastic driving. Both manuals and automatics.... clutch/flywheel and TCs are always the first to go.